The invention relates generally to injection molding and more particularly to an improved multi-cavity melt distribution manifold.
Heated manifolds which distribute melt from a single inlet to a number of spaced outlets are well known in the art. It is also well known that the length and size of the melt passage through the manifold must be equal or balanced and that sharp corners or bends can produce unacceptable shear stress in the melt. For instance, U.S. Pat. No. 4,609,138 to Harrison which issued Sep. 2, 1986 shows a drill and plug method of making manifolds. This method has the disadvantage that it is difficult to provide bends in the melt passage without sharp corners. U.S. Pat. No. 4,648,546 to Gellert which issued Mar. 10, 1987 describes making a manifold out of composite plates in which the melt passage is machined. While this does provide for the melt passage having smoothly curved bends, it has the disadvantage that leakage can result if there are a large number of cavities and very high pressures are required to fill the cavities.
These problems are overcome by using a number of manifolds in a balanced bridging arrangement as shown in U.S. Pat. No. 4,761,343 to Gellert which issued Aug. 2, 1988. However, this has the disadvantage that a number of different manifolds are required. A manifold which does provide a melt passage with smoothly curved bends and a number of radially spaced outlets by casting is shown in Gellert Canadian patent application Ser. No. 2,017,055 filed May 17, 1990 entitled "Injection Molding Cast Manifold."